This invention relates generally to gyroscopically stabilized platforms, and more specifically to combination-element gyro stabilized platform systems, and specifically to statically balanced, mechanically stabilized platform systems, such as might be used to support directional antennas in mobile applications.
A mechanically stabilized platform system is one in which a gyroscopic torsional impulse absorption system alone is used to absorb disturbing torsional impulses caused by vehicle motions. As used herein a gyroscopic torsional impulse absorption system is defined as comprising gyroscopic apparatus including at least a pair of gyroscopic rotors, means for independently mounting each of said rotors for rotation about one axis and for precession about another axis at an angle to said one axis, and a torque axis mutually perpendicular to both the rotation and precession axes, with said rotation and precession axes of each rotor being respectively parallel or perpendicular to each other so that the torque axes of both of said rotors lie in planes nominally parallel to each other and to a plane which includes centering means operatively connected to each of said axes mounting means.
Mechanically stabilized platform systems can provide a stable mounting platform for devices such as cameras, directional antennas, and sensing and recording instruments when these devices are used on ships, aircraft, and land vehicles. However, direct mechanically stabilized platforms have had only limited use in the past in such applications because they suffered from three major shortcomings: (1) they were relatively inaccurate, (2) they had large and awkward configurations, and (3) they were susceptible to destabilization from yaw/turning and other azimuth motions combined with roll or pitch motions.
One approach to mechanical stabilization in known prior art systems is to orient the platform with respect to the vertical by making the system rigidly pendulous. Examples of such rigidly pendulous systems are disclosed in U.S. Pat. Nos. 1,645,079 to Titterington, 1,083,370 to Luyken, 1,236,993 to Sperry, 1,999,897 Fieux, 2,199,294 to Seligmann, and 4,020,491 to Bieser et al. The pendular effect used to provide such systems with a long term vertical reference orientation results, however, in certain short term disturbances, caused by horizontal accelerations acting on the rigid pendulum. The short term disturbances, although attenuated by gyroscopic action, detract from the overall accuracy obtainable from a mechanically stabilized system of the rigidly pendulous type. The other major accuracy limiting effect of known systems is discussed hereinafter.
The problems associated with pendulosity are avoided by other systems such as those disclosed in U.S. Pat. Nos. 1,032,022 to Petravic, 1,573,028 to Bates, and 2,811,042 to Kenyon, by making such systems statically balanced. However, each of the foregoing systems requires periodic manual adjustment to establish a desired reference orientation. Still other U.S. Pat. Nos. including 1,906,719 to Richter, 1,324,477 to Tanner and 3,742,770 to Flannelly describes statically balanced gyroscopic systems which oriented with respect to their support frames by mechanical springs. The influence of horizontal accelerations acting on a pendulum are avoided by such systems, but in each such system the orientation of the stabilized element changes in correspondence with long term changes in support frame orientation.
U.S. Pat. No. 4,193,308 to Stuhler et al. describes a system which is statically balanced as a whole but in which the gyro assemblies are made individually pendulous. This arrangement is subject to disturbing horizontal accelerations as in rigidly pendulous systems although the horizontal accelerations act effectively at right angles to their normal directions of application.
The large and awkward configuration associated with some prior art systems typically results from constructing the platform system, including the operating equipment, as a single integrated assembly. A single integrated assembly typically requires large amounts of dead counterweight and is thus structurally inefficient. As a result, such systems are characterized by low structural resonant frequencies which result in poor tolerance to vibrations and consequent high vibration stresses on platform equipment. U.S. Pat. No. 2,924,824 to Lanctot et al. discloses a solution to this problem in a servo stabilized system through the use of push-rod assemblies. However, the push-rod assemblies are rotated together with a scanning antenna about a common axis in a integrated assembly, requiring a clear volumn of space throughout a large cylindrical area. U.S. Pat. No. 1,621,815 to Schueller proposes an arrangement which separates the overall system into two interconnected assemblies, but the yaw and turning motions of the assemblies are superimposed on both the roll and pitch axes of the stabilized platform.
A further problem in mechanically stabilized systems involves destabilization from yaw/turning motions combined with roll or pitch motions. Such destabilization results from the motions being converted into platform disturbing torques by the gyros whenever the gyro spin axes are not exactly vertical. If a gyro spin axis is exactly vertical, then rotations of the gyro support frame about the vertical axis, as in yaw or turning, will have no effect. However, if the gyro spin axis has precessed some angle away from vertical as a result of reacting to a disturbing torque about the roll or pitch axis, then a component of the gyros angular momentum will exist in the horizontal plane. If there are no motions in the horizontal plane then nothing will happen, but if horizontal rotations do occur they will be coupled into the platform by the gyro's horizontal component of momentum and will tend to mis-level the platform. Significant errors in platform orientation can occur, and in extreme cases the platform will become completely destabilized.
One approach to solving the problem of combined motions is described in U.S. Pat. No. 2,199,294 to Seligmann wherein the entire platform system is stabilized about a vertical axis relative to the meridian. In particular, the entire platform system is slaved to the meridian. A similar arrangement disclosed in U.S. Pat. No. 4,020,491 to Bieser et al. slaves the entire platform to the ship's compass. In addition, the Bieser et al. patent suggests the use of structural means to lock the gyro during rapid turning maneuvers to minimize torquing errors. Of course, if the gyros are locked or otherwise caged during turning maneuvers, they cannot react to disturbances which tend to destabilize the platform. U.S. Pat. No. 4,193,308 to Stuhler et al. describes a fluid dashpot caging system for a stabilized platform in which the entire system may be rotatably mounted on a pedestal to permit azimuth orientations of the platform. Such azimuth orientation motions, if occurring simultaneously with roll or pitch motions, would of course cause the above-described torquing errors.